a = int(input("请输入井高多少米"))
tian = 0
if a < 3:
    print("小青蛙爬出来1天都不需要！")
else:
    while a >= 0:
        a = a - 3
        if a >= 0:
            a = a + 2
            tian += 1
    print("小青蛙爬出来一共用了", tian, '天！')
